1. Technical Field
The present invention relates to a motor and a disk unit, more particularly to an inner rotor spindle motor preferred for a super-compact hard disk unit and a disk unit that employs this spindle motor.
2. Description of the Related Art
As hard disk units are getting smaller and smaller in size, it has also been required that their driving systems are reduced in size while their driving powers, as well as their strength and safety, and other properties are improved more and more.
FIG. 11 is a cross sectional view of a configuration of a spindle motor 1 of a conventional 2.5-inch hard disk unit realized to meet such the requirements. A base 2 covering the bottom portion of the spindle motor 1 entirely is formed so that its bottom portion 15 formed under a recording surface of a disk 3 and in parallel to the recording surface and a cylindrical strut portion 4 for holding a hub 5 are unitarily formed.
In a center recessed portion 4a formed so as to be surrounded by the strut portion 4 is press-fit a center shaft 6 of the hub 5 with a bearing 7 therebetween, thereby the hub 5 is rotationally held there. The hub 5, while its outer peripheral wall portion 8 is fit in a center hole 3a of each disk 3, holds three disks 3 via a supporting member 16 respectively.
On the outer peripheral surface of the strut portion 4 are disposed at equal pitches cores 17 and the predetermined number of stator coils 9 wound on the cores 17. In the inner peripheral surface of the peripheral wall 8 of the hub 5 are disposed fixedly the predetermined number of rotor magnets 10 at equal pitches. The rotor magnets 10, located closely to the stator coils 9, face the stator coils 9 respectively.
Numeral 11 denotes a disk holding spring. The spring 11 is fixed to the hub 5 by a flange 12a of a stopper screw 12 engaged with a female screw 6a formed in the center shaft 6 of the hub 5. The outer peripheral portion 13 of the disk holding spring 11 is bent towards the disk surface so as to press the extreme inner peripheral portion of each disk 3. The three disks 3 are thus held between the flange 14 formed at the lower end of the outer peripheral wall portion 8 of the hub 5 and the disk holding spring 11, so that those disks 3 are rotated unitarily with the hub 5.
According to the above mentioned configuration, all the magnetic circuits (bearings 7, cores 17, stator coils 9, and rotor magnets 10) of the spindle motor 1 are all disposed in a space generated by the outer diameter of the hub 5 substantially equal to the diameter of the center hole 3a of the disk 3 and the height of the hub 5, which is decided appropriately to hold the three disks.
Furthermore, according to the above described configuration, an outer rotor spindle motor is formed so that a stator is composed of stator coils 9 and cores 17 and a rotor is composed of the hub 5 and the rotor magnets 10, and rotor magnets are disposed outside the stator coils. And, the outer peripheral wall portion of the rotor is located inside the inner peripheral portion of the disk and the inner peripheral portion of the disk is in contact with the outer surface of the outer peripheral wall portion of the rotor.
However, if such a hard disk unit is further reduced in size so that, for example, the outer diameter is decided approximately to be 42.08 mm in height, 36.4 mm in width, and 5 mm in thickness while the configuration shown in FIG. 11 remains the same, there will arise various problems.
Concretely, when the outer diameter of the hard disk unit is reduced, the outer diameter of each disk must also be reduced. And, in order to assure a required storage capacity, that is, a certain area of the storage portion of the disk, the inner diameter of the disk must further be reduced. On the other hand, the outer diameter of the rotor cannot be reduced so much. If the outer diameter of the rotor is reduced, it is impossible to house the stator coils and the bearings in a space inside the rotor. Consequently, if the outer peripheral wall portion of the rotor is positioned inside the inner peripheral portion of the disk, the hard disk unit cannot be reduced in size satisfactorily as described above. Under such circumstances, a spindle motor constructed in accordance with the present, invention, as shown in FIG. 10, is not publicly known, and therefore is not the prior art. In this configuration, the inner peripheral portion of each disk is positioned inside the outer peripheral wall portion of the rotor. In addition, both rotor and stator are extended to a portion under the disk.
Concretely, the strut portion 51 for holding the hub 52 is formed unitarily with the base 70 in FIG. 10. The center shaft 53 of the hub 52 is press-fit in the center hole 71 formed by this strut portion 51 with a bearing 54 therebetween. Consequently, the base 70 comes to hold the hub 52 rotationally.
Furthermore, the hub 52 is provided with a center portion 56 formed so as to cover the tip of the strut portion 51 and used to place a disk 26 thereon; a planar portion 57 extended outwards in the radial direction of the disk from this center portion 56; and an outer peripheral wall portion 58 extended into the lower portion of this planar portion 57 from the outer peripheral portion. On the outer peripheral surface of the strut portion 51 are disposed the predetermined number of stator coils 60 at equal pitches. Each stator coil is wound on a core 68. On the inner peripheral coil is wound on a core 68. On the-inner peripheral surface of the outer peripheral wall portion 58 of the hub 52 are disposed the predetermined number of rotor magnets 61 at equal pitches so as to face the inner peripheral surface closely thereto.
The holding spring 62 of the disk 26 is fixed to the hub 52 by a stopper screw 64 engaged with a female screw formed in the center shaft 53 of the hub 52. At this time, the extreme outer peripheral portion 63 of the holding spring 62 is bent towards the disk surface so as to press the extreme inner peripheral portion of the disk 26. The disk 26 is thus held between the center portion 56 of the hub 52 and the holding spring 62 and rotated unitarily with the hub 52.
At the bottom of the base 70 are formed a through-hole 65 used to pull out a lead wire. 66 and a groove used to guide the lead wire 66 to external, so as to prevent the lead wire 66 from protruding from the bottom. The lead wire 66 is connected electrically to a stator coil.
The outer rotor super-compact spindle motor composed as shown in FIG. 10, however, has been confronted with various problems to be described below.
1. The thickness of the planar portion 57 of the hub 52 is limited within about 0.3 mm, so that it is difficult to form the planar portion 57.
2. The thin planar portion 57 has a large area, so that large surface vibration occurs when the hub 52 rotates.
3. Because rotor magnets are disposed outside the thin planar portion 57, the hub 52 is weak in shock.
4. It is impossible to increase the thickness of the wall of the strut portion 51 of the base for holding the bearings, the rotor section (the hub 52 and the rotor magnets 61), the disk 26, etc., so that the rigidity of the strut portion is not enough.
5. An arm for holding a head moves between the hub and the disk that rotate together. And, a clearance cannot be secured substantially enough between the hub and the disk due to the surface vibration of the hub.
6. Because the lead wire 66 is pulled out from under the base, a groove as described above must be formed unavoidably, so that the strength of the base is lowered.
7. Because the magnetic circuit extends closely under the recording surface of the disk, the planar portion 57 of the hub 52 is also used as a shielding member, thereby the shielding member cannot be formed enough in thickness and its employable material is limited. The shielding effect of the planar portion 57 is thus not enough.
Under such circumstances, it is an object of the present invention to provide a spindle motor that can be reduced in size to an extent described above.
In order to achieve the above object, the spindle motor of the present invention comprises a base member, a hub, a rotor magnet section, and a plurality of coils. The base member is composed of a bottom portion, a substantially cylindrical strut portion extended upwards from the bottom portion so as to form a column-like supporting space inside, and a substantially cylindrical peripheral wall formed so as to share the same shaft with the strut portion so that the base member forms a circular recessed portion with the peripheral wall and the bottom portion. The hub is composed of a center shaft fit in the supporting space and supported there rotationally, a joint portion extended outwards in the radial direction of the disk from the center shaft at a position higher than the top end of the strut portion, an outer peripheral wall portion connected to the joint portion and formed so as to cover the strut portion, and a supporting portion extended outwards in the radial direction of the disk from the outer peripheral wall portion so as to be able to support a hard disk. The rotor magnet section has a plurality of magnetic poles positioned lower than the supporting portion and disposed on the outer peripheral surface of the outer peripheral wall portion so that an N-pole and an S-pole are alternated along the outer peripheral surface. A plurality of coils are wound on a plurality of protruded cores extended towards the rotary shaft from the inner peripheral surface of the circular recessed portion so that their tips come close to the rotor magnet section.
It is another object of the present invention to provide a disk unit, which comprises a spindle motor and a magnetic head. The spindle motor, as described above, is composed of a rotor magnet section including a hub having a supporting portion held rotationally at the base member so as to be able to support a disk and a plurality of magnetic poles disposed so that an N-pole and an S-pole are alternated in the circumferential direction around the rotary shaft. The rotor magnet section is disposed at the hub. The spindle motor also includes a plurality of coils wound on a plurality of protruded cores disposed fixedly to the base member and extended towards the center of the rotary shaft so that their tips come closely to the rotor magnet section. The magnetic head is movable substantially in the radial direction of the disk so as to scan a recording surface of the disk placed on a disk mounting section. And, the disk unit is composed so that the tracing of the magnetic head in movement is positioned between adjacent protruded cores.
It is further another object of the present invention to provide a disk unit, which comprises a spindle motor, a scanning head, a capacitor, and power off detecting means. The spindle motor, as described above, is composed of a rotor magnet section including a hub having a supporting portion held rotationally at a base member so as to be able to support a disk and a plurality of magnetic poles disposed so that an N-pole and an S-pole are alternated in the circumferential direction around a rotary shaft. The rotor magnet section is disposed at the hub. The spindle motor also includes a plurality of coils wound on a plurality of protruded cores disposed fixedly to the base member and extended towards the center of the rotary shaft so that their tips come closely to the rotor magnet section. The scanning head is held movably by moving means substantially in the radial direction of the disk so as to scan a recording surface of the disk. The capacitor accumulates an electrical energy when the disk unit is powered. The power off detecting means detects a power off of the power of the disk unit. And, the disk unit is composed so that the electrical energy of the capacitor is supplied to the moving means according to a power off detected by the power off detecting means, thereby the scanning head is moved to a predetermined unloading position.